Paul,
The exact frequency of the 4 MHz (nominal) reference oscillator may be
slightly different than exactly 4 MHz.
If you have a well calibrated external frequency counter, you can adjust
the 4 MHz reference (adjust C22) by measuring the frequency at TP1 with
both the internal counter and the external counter - adjust C22 until
the internal counter reads the same as the external counter.
Another method that provides even greater accuracy is the method
outlined on the Elecraft website on the Builder's Resource page -
http://www.elecraft.com/Apps/K2%20C22%20Adjust%20App%20Note.pdf.
This method requires no extra calibrated equipment, but there is a
requirement that the standard station be tuned with precision. When
using WWV, I use Spectrogram to observe the audio output tones, knowing
that WWV transmits tones of 500 and 600 Hz on alternate minutes (there
are silent minutes and one minute of 440 Hz tone as well). If the tones
line up with my Spectrogram markers at 500 and 600 Hz, I know that WWV
is properly tuned within one or two Hz.
After setting the 4 MHz reference, run CAL PLL and CAL FIL changing each
BFO and the resulting frequency should be within 20 Hz of the correct
dial reading.
For more information, please refer to my website article on K2 Dial
Calibration www.qsl.net/w3fpr
73,
Don W3FPR
paul wrote:
Hi,
Recently I started to upgrade my K2 (sn 2592) with the KPA100 kit. Before
I could complete the KPA100 though, I had to upgrade the K2 from rev A to
rev B. I have completed all the revs except for the firmware upgrade -
Elecraft sent only the MCU but not the IOC. It is now being mailed.
Before the rev, the frequency on the dial matched the received frequency.
Now WWV is received on 10.012 MHz. I have done the calibration of the 4MHz
several times - checking with a known good receiver (AOR AR7030+). I can
vary the c22 and zero beat exactly on frequency (USB and LSB) - also at
higher harmonics (16Mhz). I ran an antenna wire next to the 4MHz xtal and
listen on the SW receiver.
After the 4MHz calibration, I have run the CAL PLL and then modified every
CAL FIL entry afterwards. Still no change. The dial reads 7.010Mhz when
hearing 7MHZ and 14.020Mhz when hearing 14Mhz.
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